2011-2015: hottest 5-year period on record

This is the Globe’s Hottest Five-Year Period on Record

ClimateCentral.org, Nov. 25, 2015

No matter how you stack it, the first half of the 2010s will be remembered for its record heat. The five-year period from 2011-15 has been the hottest such period ever recorded. And with last year setting the hottest year mark, only to be surpassed by a wide margin this year, it’s clear that the planet has changed.

Ahead of the Paris climate talks, the World Meteorological Organization released its annual state of the climate report on Wednesday. It documents the excessive heat that’s been building up around the world and causing changes from the depths of the oceans to the top of the atmosphere.

“The state of the global climate in 2015 will make history as for a number of reasons,” Michel Jarraud, the head of the WMO, said. “2015 is likely to be the hottest year on record with ocean surface temperatures at the highest level since measurements began. It is probable that the 1°C threshold will be crossed. This is all bad news for the planet.”

A Climate Central analysis attributed almost all of 2015’s record heat to carbon pollution from human activities with El Niño and other natural phenomenon also playing smaller roles. The year-to-year horse race of warmest years, while an indicator of global warming, also includes some noise. That’s why the WMO looked at five-year periods, which offer a more robust look at the changes occurring to our planet.

The finding that it’s been the hottest five-year period on record on land and at sea underscores the need to reduce carbon emissions in an effort to avoid further dramatic changes. The WMO warned that continuing on a business as usual path of rising emissions could put the world on track for 10.8°F (6°C) increase in the global average temperature.

There are also concerns that oceans, which currently absorb more than 90 percent of the extra heat being trapped by human greenhouse gas emissions, could eventually release some of that back to the surface, speeding up the surface temperature rise.

Beyond the long-term record, the past five years have been punctuated by extreme heat events around the globe, the most recent being an extreme heat wave in India this summer that left 2,500 dead. Other notable examples of extreme heat during that period have increasingly been linked to climate change.

All of this has occurred as atmospheric carbon dioxide (CO2) levels have continued to rise. Last week might have been the last time CO2 was below 400 parts per million in our lifetimes, underscoring that the impacts of climate change are here to stay for decades to come even if a strong climate deal is reached in Paris.